Image diagnostic devices used in medical practice such as an ultrasonic device, a CT (Computed Tomography) device, and an MRI (Magnetic Resonance Imaging) device have been widely spread as means to image tissue in a living body. A dedicated contrast medium has been developed for each diagnostic device, and information related to the dynamic state of a bloodstream that cannot be generally imaged can be obtained by using the contrast medium.
A liver tumor is one of lesions for which observation of the bloodstream dynamic state is especially effective. Regarding the liver tumor, a known fact is that portal vessels governing the lesion part are transited to artery vessels in the course in which the liver tumor is deteriorated from a precancer state such as hepatitis or cirrhosis to liver cancer. In the case of the liver tumor at an early stage, a known fact is that portal vessels in which blood having flowed through a digestive system flows are dominant. However, as the disease progresses, artery vessels become dominant (Non-patent document 1).
The artery vessels are different from the portal vessels in the start time of contrast or the inflow rate of the contrast medium due to a difference between circulation routes. Therefore, an early stage of contrast and the next stage thereof are expressed as an artery phase and a portal phase, respectively, in a contrast inspection in some cases. A time intensity course obtained by plotting time changes of brightness along with inflow of the contrast medium is useful in evaluating such a difference of the bloodstream dynamic state. Using a contrast image of the lesion part or the time intensity course, the lesion can be promptly detected and the activation level can be determined. Further, the contract inspection is considered to be important as an effective imaging technique in a differential diagnosis for a lesion because the bloodstream dynamic state is changed depending on the type of lesion such as hepatocellular cancer, metastatic cancer, or a cyst.
In addition, the evaluation of the bloodstream dynamic state is effective in determining the effect of cancer treatment. In the case of RF treatment or medical therapy using medicine, the bloodstream dynamic state is an important target for observation other than the size of a tumor. This is because even if the size of a tumor is not changed on an image, the effectiveness of the treatment can be determined on the basis of disappearance of tumor vessels or a decrease in blood flow. Especially, in the case of a treatment method targeting vessels serving as nutrient supply routes to a tumor such as an angiogenesis inhibitor or vascular embolization therapy, not only the presence or absence of a bloodstream to the lesion, but also the bloodstream dynamic state becomes an important target for observation in the determination of the effect because in the case where the bloodstream can be observed, the following treatment policy is changed depending on whether the bloodstream is of artery or portal.
As described above, when the bloodstream dynamic state is evaluated to obtain information useful in a differential diagnosis or in the determination of the treatment effect, it is important to discriminate the artery phase from the portal phase using a series of contrast processes such as the start of inflow of the contrast medium into the artery vessels or the portal vessels. Patent documents 1 and 2 are relevant prior arts. The content described in Patent document 1 relates to a technique of evaluating the angiogenesis of a tumor, and is a method of modeling measurement values with a model curve. The content described in Patent document 2 relates to a system that calculates the average speed of a bloodstream by associating a function having S-shaped characteristics with a time function representing a contrast process. According to the content described in Patent document 2, the reflux of a contrast medium to tissue again is associated with an S-shaped function, and the average speed or average flow rate of a bloodstream at the time of reflux is estimated.